All 3 Uses

antagonist
in
Far from the Madding Crowd
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That stillness, which struck casual observers more than anything else in his character and habit, and seemed so precisely like the rest of inanition, may have been the perfect balance of enormous antagonistic forces—positives and negatives in fine adjustment.†
Chpt 16-18

antagonistic = with opposition or hostility
You are my antagonist, with this difference from real warfare, that I shall miss you every time by one hair's breadth, or perhaps two.†
Chpt 28-30 *

antagonist = someone who offers opposition or is hostile
Whether from a purely mechanical, or from any other cause, when Bathsheba arose it was with a quieted spirit, and a regret for the antagonistic instincts which had seized upon her just before.†
Chpt 43-45

antagonistic = with opposition or hostility

Definitions:

(1) (antagonist as in: the antagonist in the film)
someone who offers opposition or is hostile
(2) (meaning too rare to warrant focus)
Specialized Definitions of antagonist:
- literature or storytelling: the most important character who opposes the main character or protagonist
- physiology: a muscle that relaxes when another muscle contracts
- chemistry and biology: a substance that interferes with the effect of another substance